Atomic force microscopes (AFMs) are high-resolution surface measurement instruments. The construction of a typical AFM is described in detail in several U.S. patents, including U.S. Pat. No. 4,935,634 to Hansma et al, U.S. Pat. No. 5,025,658 to Elings et al, and U.S. Pat. No. 5,144,833 to Amer et al.
The typical AFM includes a probe that has a cantilever and a single probe tip extending from the cantilever. In order to measure the topography of the surface of a sample, for example, the AFM scans the probe with respect to the surface. The scanning motion can be produced by translating either the sample or the probe.
As the probe is scanned over the surface, atomic forces interact with the probe tip and cause the cantilever to deflect. By measuring the deflection of the cantilever as a function of probe position with respect to the surface, a three dimensional map of the surface can be created.
In addition to measuring surface topography, AFM's are often used to perform other types of tasks. For example, AFM's can be used to measure conductivity variations across very small areas in a sample. This type of measurement may be referred to as a “conductive AFM measurement”. A “tunneling AFM measurement” (which uses very low currents) is considered herein as a special type of C-AFM measurement.
Because of their resolution and versatility, AFM's are important measurement instruments and have found uses in many diverse fields ranging from semi-conductor analysis to biological research.
It would be desirable, however, to expand the functionality of AFM'S. It would also be desirable to increase the utility and accuracy of AFM measurements.